Numerical Modeling of Thermal Behaviors and Vertical Motions of Polar Patrol Balloon with Auto-Ballasting System.

Abstract

A time-dependent numerical model has been developed to investigate vertical motions of a zero-pressure balloon with an auto-ballasting system. This model is applied to the data of a Polar Patrol Balloon (PPB) experiment in January 1990, and the following results are obtained: (a) The balloon behaviors can be described by four periods in a day (post-noon descending, night ballasting, morning ascending, and pre-noon expulsion) and three stages during a flight (ballasting without sunset, ballasting with sunset, and no ballasting with sunset). (b) Two main factors determine the daily ballasting amount. One is the noon-midnight difference of the temperature ratio between the interior gas and the ambient air, and the other is the weight of the interior gas. The ballasting amount increases as the balloon approaches the latitude region where sunset exists, and decreases after it enters the region. (c) The vertical motions and the daily ballasting amount are strongly influenced by the radiative properties of the interior gas, especially by its absorptivity for the visible wave radiation. (d) While the auto-ballast control is operated, the maximum altitude of the balloon increases day by day, and after the control is terminated, both the maximum and minimum altitudes decrease day by day. These altitude changes can be explained by the ballasting and leakage of the interior gas. Differences between the model calculations and the observations are also discussed.